Cowser (thumb) will begin a rehab assignment with High-A Aberdeen on Wednesday, Matt Weyrich of The Baltimore Sun reports.
Cowser is finally ready to play some rehab games after fracturing his left thumb back in late March. The 25-year-old is on the 60-day injured list and not eligible for activation until May 30, but he would seem to have a good shot to return to the Orioles' outfield that day if his rehab assignment goes off without setbacks.